1. Field of the Invention
This invention relates to froth flotation, including a froth flotation column consisting of a plurality of stages.
2. Description of the Prior art
Froth flotation has been used for many years for beneficiating mineral materials, and more recently for waste water treatment. Generally, in a flotation process solid particles or liquid droplets such as oil are separated from pulp or an aqueous phase. The flotation process includes generating gas bubbles and dispersing them in the pulp or aqueous phase to be treated. The gas bubbles contact and capture suspended particles or droplets in the pulp or aqueous phase. Due to the buoyancy of the gas bubbles, the gas bubbles with captured particles or droplets rise into a froth layer which floats on the surface of the pulp or aqueous phase. The froth layer is removed by an overflow skimming process.
In typical operations of conventional froth flotation devices, a single unit vessel is used for aerating the pulp and for effecting separation of froth. Generally, mechanical mixing is required which is energy intensive. The overall separation efficiency of the conventional single unit flotation device is inherently limited because it is difficult to optimize the mixing and contacting between the gas bubbles and the suspended fine droplets or solid particles.
Flotation columns are more efficient and economical than the conventional mechanical flotation devices. The main advantages of the flotation column include improved overall separation efficiency, simple construction and lower operating costs; however, even flotation columns may not be sufficiently efficient for all waste separation or treatment operations. For example, conventional froth flotation apparatus, including flotation columns, are not efficient for separating very fine solid particles or treating emulsified oily waste water. Therefore, there remains a need for an effective and low cost flotation device for waste water treatment and fine mineral beneficiation. An article entitled "Flow in Froth Zone of a Flotation Column" in the Canadian Metallurgical Quarterly, Volume 29, No. 2, April-June, 1990, pp. 97-103, indicated that in recent years many industries are replacing their conventional machines with flotation columns.
Column flotation apparatus is disclosed in a number of issued patents, including the following: U.S. Pat. Nos. 4,592,834, 4,804,460, 4,938,865, 4,940,534, 4,966,687, 4,971,731, 5,078,921, 5,116,487, 5,122,261, 5,167,798, 4,981,582, 5,249,668 and 5,096,572.